US20080255608A1 - Tool with end effector force limiter - Google Patents

Abstract

The invention provides surgical or diagnostic tools and associated methods that offer improved user control for operating remotely within regions of the body. In some embodiments these tools include a proximally-located actuator for the operation of a distal end effector, as well as proximally-located actuators for articulational and rotational movements of the end effector. Control mechanisms and methods refine operator control of end effector actuation and of these articulational and rotational movements. A force limiter mechanism protects the end effector and manipulated objects from the harm of potentially excessive force applied by the operator. The tool may also include other features. A multi-state ratchet for end effector actuation provides enablement-disablement options with tactile feedback. An articulation lock allows the fixing and releasing of both neutral and articulated configurations of the tool and of consequent placement of the end effector. A rotation lock provides for enablement and disablement of rotatability of the end effector.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• This application is related to the following concurrently filed US patent applications: “Tool with articulation lock” of Hegeman, Danitz, and Alvord, “Tool with multi-state ratcheted end effector” of Hinman, “Tool with rotation lock” of Hinman and Danitz, and “Articulating tool with improved tension member system” of Hegeman, Danitz, Bertsch, and Alvord.
INCORPORATION BY REFERENCE
• All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.
FIELD OF THE INVENTION
• This invention relates to tools with end effectors whose actuators control aspects of end effector operation.
BACKGROUND OF THE INVENTION
• The popularity of minimally invasive surgery has been growing rapidly due to its association with decreased complication rates and post-surgical recovery times. The instruments employed are generally hand-operable and typically include a handle, a shaft that may or may not be rotatably attached to the handle, a rotation knob rigidly fixed to the proximal end of the shaft near the handle in instances where the shaft is rotatably attached to the handle, and a tool or end effector attached to the distal end of the shaft. To manipulate the instruments, they are held at the handle and typically pivoted about a pivot point defined by the entry incision, i.e., the incision made in the abdominal wall for laparoscopic procedures. The end effector may also be rotated about the shaft axis, as for example, by rotating a rotation knob, if present. In use, these instruments have limited control and range of motion and become physically taxing as the length of the procedure increases.
• Surgical procedures such as endoscopy and laparoscopy typically employ instruments that are steered within or towards a target organ or tissue from a position outside the body. Examples of endoscopic procedures include sigmoidoscopy, colonoscopy, esophagogastroduo-denoscopy, and bronchoscopy, as well as newer procedures in natural orifice transluminal endoscopic surgery (“NOTES”). Traditionally, the insertion tube of an endoscope is advanced by pushing it forward, and retracted by pulling it back. The tip of the tube may be directed by twisting and general up/down and left/right movements. Oftentimes, this limited range of motion makes it difficult to negotiate acute angles (e.g., in the rectosigmoid colon), creating patient discomfort and increasing the risk of trauma to surrounding tissues.
• Laparoscopy involves the placement of trocar ports according to anatomical landmarks. The number of ports usually varies with the intended procedure and number of instruments required to obtain satisfactory tissue mobilization and exposure of the operative field. Although there are many benefits of laparoscopic surgery, e.g., less postoperative pain, early mobilization, and decreased adhesion formation, it is often difficult to achieve optimal retraction of organs and maneuverability of conventional instruments through laparoscopic ports. In some cases, these deficiencies may lead to increased operative time or imprecise placement of components such as staples and sutures.
• Recently, surgical instruments, including minimally invasive surgical instruments, have been developed that are more ergonomic and which have a wider range of motion and more precise control of movement. These instruments may include mechanisms that articulate using a series of links coupled with one or more sets of tension bearing members, such as cable. As with conventional instruments used in minimally invasive surgery, rotation of the shaft and end effector with respect to the handle is an important feature of cable and link type instruments to aid with dissecting, suturing, retracting, knot tying, etc. Ergonomic, flexible, and intuitive mechanisms that facilitate manual control of the end effectors of such instruments are also important factors as medical procedures become more advanced, and as surgeons become more sophisticated in their operating abilities. Further improvements in the features and design of surgical instruments are desirable.
SUMMARY OF THE INVENTION
• Some surgical or diagnostic instruments have an end effector whose operation is controlled by a movable end effector actuator. In particular, some instruments have operation states in which a force applied to the end effector actuator may be reflected in a force delivered by the end effector. It may at times be desirable to limit the force delivered by the end effector, regardless of the amount of force applied to the end effector actuator. This invention provides methods and devices for limiting the force delivered by an end effector.
• Some embodiments of the invention comprise a surgical or diagnostic tool comprising an end effector at a distal end of the tool and an end effector actuator at a proximal end of the tool. The end effector actuator is operatively connected to the end effector through a linkage to deliver an actuation force from the end effector actuator to the end effector in response to movement of the end effector actuator. The tool further comprises a force limiter adapted to establish an upper limit on the actuation force that may be delivered to the end effector by the end effector actuator.
• In some embodiments, the tool further comprises a handle supporting the end effector actuator, the end effector actuator being movable with respect to the handle. The tool may comprise a stop element engagable with the end effector actuator to stop its motion. In some embodiments, the force limiter is adapted to deform in response to actuation force delivered by the end effector actuator.
• Some embodiments of the force limiter comprise a spring in the linkage. The spring may be pre-loaded to a predetermined stress within the linkage. The spring may be formed from a superelastic shape memory material treated so as to bend when the upper limit of the actuation force is applied to the end effector by the end effector actuator. The superelastic shape memory material may have a plateau stress level, and the spring may be disposed within the linkage so at to be pre-loaded at least about to the plateau stress level. The tool may include both a spring and a stop element engagable with the end effector actuator to stop its motion.
• In some embodiments, the end effector is operably connected to the end effector actuator at least in part through the force limiter. The force limiter may be disposed between the end effector actuator and the linkage. In some embodiments, the end effector actuator is operably connected to the linkage such that movement of the end effector actuator moves the linkage. Movement of the end effector actuator with respect to the linkage may vary when the upper limit of the actuation force is reached.
• In some embodiments the force limiter comprises a tension bearing member in the linkage. In some of these embodiments, the tension member includes a superelastic shape memory material that may be pre-stretched to a predetermined stress when assembled into the linkage. In some typical embodiments, the predetermined stress may correspond approximately to the upper limit of the actuation force that is to be applied to the end effector by the end effector actuator.
• In some embodiments, the end effector comprises a movable force delivery surface, and in some embodiments, the end effector may comprise a pair of jaws. In some embodiments, the tool comprises a shaft disposed between the end effector and the end effector actuator. The tool may also comprise an articulation mechanism for manipulating angular orientation of the end effector with respect to the shaft. The articulation mechanism in turn may comprise a proximal link and a distal link spaced apart from the proximal link. In such embodiments, movement of the proximal link causes corresponding relative movement of the distal link and angular movement of the end effector with respect to the shaft.
• Embodiments of the invention comprise a method of operating a surgical or diagnostic tool, the tool as summarized above, where the method of use comprises placing the end effector at a target site, applying an actuation force to the end effector actuator, delivering at least some of the actuation force through the end effector to the target site, and limiting the magnitude of the delivered actuation force to an upper limit.
• The step of applying an actuation force may comprise moving the end effector actuator. In some embodiments, the tool used in the method further comprises a handle supporting the end effector actuator, and the step of moving the end effector actuator comprises moving the end effector actuator with respect to the handle. The tool may comprise a stop element, and the moving step may then comprise engaging the end effector actuator with the stop element.
• The method of using a surgical or diagnostic tool, as summarized above, may include the use of a tool that further comprises a force limiter, and the limiting step of the method may further comprise deforming the force limiter. The force limiter may comprise a spring, and the limiting step may then comprise deforming the spring. In some embodiments, the deforming step comprises increasing strain of the spring without substantially increasing stress of the spring. In other embodiments, the force limiter comprises a tension bearing member, and the limiting step may include tensioning the member. In some of these embodiments, the deforming step may include the tension member stretching in response to the tensioning. In some of these embodiments, the step of limiting the magnitude of the delivered actuation force includes the stretching of the tension member.
• The step of delivering the force may comprise moving the end effector, and the limiting step may comprise ceasing movement of the end effector despite continued movement of the end effector actuator. In some embodiments, the end effector comprises jaws, and the step of delivering a force to the target site comprising moving the end effector jaws.
• In some embodiments of the method of use, the tool further comprises a handle supporting the end effector actuator and a shaft disposed between the handle and the end effector, and the method further comprises moving the handle angularly with respect to the shaft to move the end effector angularly with respect to the shaft.
BRIEF DESCRIPTION OF THE DRAWINGS
• The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings which are briefly described below.
• FIG. 1 is a front perspective view of an articulatable surgical tool.
• FIG. 2 is perspective view of a surgical tool in an articulated position.
• FIG. 3 is an exposed side view of a surgical tool with an end effector actuator and an end effector both in an open position.
• FIG. 4 is an exposed side view of a surgical tool with an end effector actuator and an end effector both in a closed position.
• FIG. 5 is a side view of the proximal portion of a tool, showing the handle and proximal end of the shaft, with an articulation locking sleeve in a distal and unlocked position.
• FIG. 6 is a side view of the proximal portion of a tool, showing the handle and proximal end of the shaft, with an articulation locking sleeve in a proximal and locked position.
• FIG. 7 is an exposed view of a portion of a tool from an overhead distal looking perspective, the portion including the handle, locking rotation knob, and a proximal link.
• FIG. 8 is a cutaway view of a portion of the handle, knob, and a proximal link.
• FIG. 9 is an exposed view of a handle from a distal-looking perspective.
• FIG. 10 is an exposed view of a handle from a proximal-looking perspective.
• FIG. 11 is an exposed side view of a surgical tool with an end effector actuator and an end effector both in an open position, the end effector jaws embracing an object.
• FIG. 12 is an exposed side view of a surgical tool with an end effector actuator in a closed position and the end effector in an open position, the end effect or jaws embracing an object, the force applied by the closed end effector actuator having been absorbed by a force limiter.
• FIG. 13 is a cross sectional view of the force limiter locale within the handle of a tool, showing the end effector actuator, force limiter, and rod actuator, the end effector actuator in an open position, the force limiter minimally bent at preload tension.
• FIG. 14 is a cross sectional view of the force limiter locale within the handle as inFIG. 13, except the end effector actuator is in a closed position, the force limiter is fully bent, absorbing force from the closed end effector actuator.
• FIG. 15 is a side perspective, slightly distal-looking view of a rotatable rod actuator, a ledge that engages the force limiter at the bottom.
• FIG. 16 is a side perspective, more sharply distal-looking view of a rotatable rod actuator, a ledge that engages the force limiter at the bottom.
• FIG. 17 is a cross sectional view of the force limiter locale of an instrument showing the end effector actuator in an open position, and the force limiter having a minimal bend.
• FIG. 18 is a cross sectional view of the force limiter locale of an instrument with the showing the end effector actuator in an closed position, and the force limiter having absorbed force from the closure of the end effector actuator, and thereby bent.
• FIG. 19 is a view of the force limiter locale of an instrument, similar to the view provided inFIGS. 17 and 18, but with a different embodiment of a force limiter spring.
• FIG. 20 is a cross sectional side view of a force limiter locale in a tool, wherein the force limiter is embodied as a linear actuator for an end effector actuating rod.
DETAILED DESCRIPTION OF THE INVENTION
• The invention described herein relates to a force limiter mechanism intervening between force applied by a user at the proximal end of a tool and the transmission of that force to the distal end of a tool. Embodiments of the invention may be applied to non-articulating instruments, but many typical embodiments are applied to the operation of articulating tools. Steerable articulating instruments are described in U.S. Pat. No. 7,090,637; US 2005/0107667; US 2005/0273084; US 2005/0273085; and US 2006/0111210. The articulating mechanisms of the tools described in those publications use multiple pairs of segments or links controlled, e.g., by multiple sets of cables. Depending upon the specific design of the device, the links can be discrete segments (as described, e.g., in U.S. Pat. No. 7,090,637) or discrete portions of a flexible segment (as described, e.g., in US 2005/0173085). The instrument may also include steerable or controllable links of various types, e.g., as described in US 2005/0273084, US 2006/0111209, and US 2006/0111210. Some articulating or steerable instruments have an articulating capability provided by minimal numbers of link pairs and cables connecting such links, U.S. Pat. No. 5,916,146 of Alotta, for example, has a mechanism comprising a single pair of links controlled by a single cable.
• When using such articulating instruments, a user may manipulate the proximal end of the instrument, thereby moving one or more proximal links of the articulation mechanism. This movement results in relative movement of the distal link(s) corresponding to the proximal link(s). It may at times be desirable to lock or otherwise maintain the straight or bent shape of the instrument. In certain embodiments of this invention, the shape of the instrument is maintained by preventing movement of at least one of the proximal links with respect to the rest of the instrument. In other embodiments, a friction-based articulation locking mechanism locks all links, proximal and distal; these embodiments are disclosed in the concurrently filed and hereby incorporated application “Tool with articulation lock” of Hegeman, Danitz, Hinman, and Alvord.
• Many articulating instruments have end effectors controlled by movable actuators; a movable end effector actuator may be, for example, a moveable portion of the handle of an instrument, or a thumbpiece. In some embodiments, the end effector actuator has an operation state in which movement is permitted in only one direction and an operation state in which the actuator is free to move in two or more directions. Certain embodiments of this invention provide methods and devices for changing the operational state of an end effector actuator between a state in which movement of the actuator is permitted in only one direction; a state in which the actuator is permitted to move in two directions in response to continuous user input to a state changer; and a state in which the actuator is permitted to in two directions in the absence of user input to a state changer.
• FIGS. 1-20 show embodiments or portions of anarticulatable tool100 with anend effector102 at its distal end and anend effector actuator104 within ahandle106 at its proximal end.Instrument100 may be used, e.g., in a laparoscopic procedure requiring grasping or cutting within a patient. Proximal articulation links108 and110 extend distally fromhandle106, and distal articulation links112 and114 extend proximally fromend effector102.Proximal link108 is connected to and moves withhandle106. Likewise,distal link112 is connected to and moves withend effector102. Abushing115 separateslinks110 and112.Bushing115 has convex surfaces at its proximal and distal ends that engage with corresponding concave surfaces onlinks108 and110. Further details of ball and socket links suitable for use with this invention may be found in US 2005/0273084, US 2006/0111209, and US 2006/0111210. Anelongated shaft116 is disposed between the proximal links and the distal links. Embodiments of the shaft may either be rigid or flexible, although embodiments shown herein are depicted as being rigid.
• As seen inFIGS. 3 and 4, a set ofcontrol cables118 is attached toproximal link108, extends throughproximal link110,shaft116 anddistal link114, and is attached todistal link112. A second set ofcontrol cables120 is attached toproximal link110, extends throughshaft116 and is attached todistal link114. In this embodiment, there are threecontrol cables118 in the first set and threecontrol cables120 in the second set. It should be appreciated, however, that other numbers of control cables may be used to connect corresponding proximal and distal links. In addition, mechanisms other than cables may be used to connect corresponding links.
• As shown inFIG. 2, movement ofhandle106 andproximal link108 with respect toproximal link110 movesend effector102 anddistal link112 in a relative and corresponding manner. Likewise, movement ofproximal link110 with respect toshaft116 movesdistal link114 with respect toshaft116 in a relative and corresponding manner, also as shown inFIG. 2. This relative articulation movement provides a way for a user to remotely manipulate the end effector through movement of the handle. The relative movement of the distal link that corresponds to the proximal link movement may either mirror the movement of the proximal link or be reciprocal to it, depending on whether the cables are strung directly (for reciprocal movement), or whether they are rotated 180 degrees (for mirrored movement) between the proximal and distal links.
• In order to maintain a particular position of the end effector with respect to the shaft, the articulating tool of this invention may have an articulation lock. In the embodiment shown inFIGS. 1-6, the articulation lock includes a movablerigid sleeve130. In the unlocked position shown inFIGS. 1-5,sleeve130 is distal toproximal links108 and110. In the locked position shown inFIG. 6, however,sleeve130 has been moved proximally to a position adjacent to and coveringlinks108 and110 as well as the proximal end ofshaft116, thereby blocking relative movement betweenlinks108 and110 and betweenlink110 andshaft116. In this locked position, relative movement betweendistal links112 and114 and betweenlink114 andshaft116 is prevented as well.
• As shown inFIG. 6, asleeve support mechanism132 extends proximally fromshaft116 to provide sliding support forsleeve130. Adistal stop134 provides a limit of distal movement ofsleeve130; a similar stop (not shown) is provided on or withinhandle106 to limit proximal movement ofsleeve130. Detents, ridges or other mechanisms may be provided to maintain the sleeve in its proximal or distal positions and to provide tactile feedback to the user regarding the position of the sleeve. Further detail on mechanisms that control permissibility of articulation in articulatable instruments is provided in the concurrently filed and hereby incorporated U.S. patent application entitled “Tool with articulation lock” of Hegeman, Danitz, Hinman, and Alvord.
• The description now turns briefly to features of tools that include embodiments of an inventive force limiter, such features including rotatability of the distal end effector by proximal mechanisms, and mechanisms by which rotatability is allowed or disallowed by a locking mechanism. Provided here will be a brief description of some these embodiments; a full disclosure of such embodiments is provided in concurrently filed and hereby incorporated U.S. patent application entitled “Tool with rotation lock” by Hinman and Danitz.
• Theend effector102 oftool100 may be rotated with respect to handle106 and then locked so that further rotation betweenend effector102 and handle106 is prevented. Arotation knob101 is disposed at least partially aroundlink108. In the locked position,teeth103 formed on the proximal face ofknob101 engage correspondingteeth105 formed on a distal face ofhandle106, as seen inFIG. 10. Handle106 may be made in two pieces; two views of one of the two pieces are shown inFIGS. 9 and 10.) In this embodiment, the rotation lock is self-locking due to the action of aspring107biasing knob101 proximally into engagement withhandle106, as shown inFIG. 8.
• When moved distally against the bias ofspring107, theteeth103 ofknob101 disengage from theteeth105 ofhandle106. This disengagement permitsknob101,links108 and110,shaft106,links112 and114, andend effector102 to rotate with respect to handle106. This action permits the end effector to be rotated in any articulated configuration. When the end effector has been rotated the desired amount, release ofknob101 permits the two sets of teeth to re-engage, thereby locking the device against further rotation. In one embodiment,knob101 is made in two pieces, aninner member109 and anouter member111, as shown inFIG. 8. Theteeth103 are formed on theinner member109. Indentations or knurls113 (FIG. 7) may be formed onknob101 to facilitate grasping.
• Description now turns to consideration of a force limiter that intervenes in the transmission of force from a user to an end effector on a tool. In the embodiments illustrated inFIGS. 1-20, theend effector102 is a pair of jaws. Other end effectors (surgical, diagnostic, non-medical mechanical manipulators, etc.) and end effector actuators may be used with the articulating tool of this invention. Actuation force is transmitted from movableend effector actuator104 through a transmission or linkage that includes arotatable rod actuator122, amovable rod terminator124, and a tension bearing member, such asrod125 connected torod terminator124, as shown inFIGS. 3,4,7, and8.Rod125 passes throughlink108,bushing115, link110; the shaft (not shown inFIG. 8) and the distal links (not shown inFIG. 8) to reach and actuate the end effector.Rod terminator124 encases a portion ofrod125 withinhandle106 to prevent therod125 from buckling under a compressive load. Similar features may be provided throughout thetool100 to laterally constrainrod125. (See further detail in concurrently filed patent application “Articulating tool with improved tension member system” of Hegeman, Danitz, Bertsch, and Alvord).End effector actuator104 androd actuator122 are both rotatably mounted on acommon bushing202 so as to be able to be rotated with respect to each other to moverod125 and thereby actuateend effector102.
• A force limiter such as aleaf spring200 attached to endeffector actuator104 extends to a ledge204 (shown best inFIGS. 15 and 16) formed inrod actuator122 and provides for force transmission from theend effector actuator104 torod actuator122 asactuator104 is moved towardhandle grip206.Actuator104 may be moved until astop element208 on a surface ofactuator104 engages astop element210 ongrip206, as shown inFIGS. 3 and 4 and inFIGS. 11 and 12. InFIG. 4, the end effector jaws are closed whenactuator104 engagesstop element210. InFIG. 12, on the other hand, the jaws have encountered anobject212. The force limiter of this invention permits theactuator104 to continue moving towardstop element210 even if the jaws have stopped closing while limiting the amount of force applied by the end effector on the object, as explained below.
• Spring orforce limiter200 rotationally biases therod actuator122 against theend effector actuator104 such thatsurface250 ofrod actuator122 contacts surface252 ofend effector actuator104 as shown inFIG. 13. In this embodiment,force limiter200 is formed from a shape memory material (such as Nitinol) that is in its superelastic state.Force limiter200 is pre-biased (to, e.g., 1.5% strain) so that it is at a known state along its stress/strain curve. This pre-loading ofspring200 ensures that, until a predetermined threshold force is reached (as described below),end effector104,spring200,bushing202, androd actuator122 all move together and act as a rigid body. If the jaws ofend effector102 encounter an obstacle (as shown inFIG. 12) and the force applied throughactuator104 exceeds the threshold force, the stress onforce limiter200 reaches the characteristic plateau of the stress/strain curve, andforce limiter200 bends elastically substantially without delivering any further rotational movement torod actuator122, as shown inFIG. 14.
• In one embodiment, the instrument has aforce limiter200 that establishes an upper limit on the actuation force that may be delivered to the end effector by the end effector actuator.
• In one embodiment,spring200 may be formed from an elastomeric or spring metal material. In other embodiments, the material used to formspring200 is selected and/or treated to provide a stress-strain relationship with a characteristic plateau region in which stress does not substantially change over a range of strain values. For example, in the instrument shown inFIGS. 1-19,spring200 is formed from a superelastic shape memory material, such as Nitinol. The Nitinol is selected and treated so thatspring200 is in the Austenitic phase at the temperatures at which the instrument will be used. The material properties when so treated provide for substantially no change in stress over a range of strain values, e.g., 1.5% to 6% strain.
• When assembling the instrument,spring200 may be pre-loaded so that its strain is at or near the beginning of the stress plateau. In the absence of any counterforce resisting closing of the jaws ofend effector102, movement ofend effector actuator104 towardhandle grip206 transmits an actuation force throughspring200 torod actuator122,rod terminator124,rod125, and finally to endeffector102. As shown inFIGS. 11 and 12, if the jaws ofend effector102 encounter anobject212,actuator104 will experience a counterforce as it continues its movement towardgrip206. When the counterforce exceeds the characteristic plateau stress ofspring200,spring200 will deform without substantially increasing the strain ofspring200, thereby maintaining the actuation force transmitted throughspring200 and the remaining components of the actuation linkage. In the illustrated embodiment, thematerial comprising spring200 may be selected and/or treated so that the spring remains in the stress plateau throughout its range of motion up to and including the point at which end effector actuator meets thelimit stop210 ongrip206.
• Description now turns briefly to an actuator movement controller that may be included in embodiments of the invention depicted inFIGS. 1-20. Embodiments may include a shaft having a proximal end and a distal end, an end effector at the distal end of the shaft, a movable end effector actuator at the proximal end of the shaft and operably connected to the end effector, and an actuator movement controller operably connectable to the end effector actuator. The actuator movement controller includes a user-activated state changer that is changeable among several states. These states include ones in which the movement controller is (1) enabled and engaged with the end effector actuator to prevent movement of the end effector actuator in at least one of two opposing directions, (2) enabled and disengaged from the end effector actuator to permit movement of the end effector actuator in a first direction and a second direction opposite to the first direction in response to continuous user input via the state changer, and (3) disabled to permit movement of the end effector actuator in a first direction and a second direction opposite to the first direction in the absence of user input via the state changer. In some embodiments, the first state (enabled and engaged) may prevent movement of the end effector actuator in both directions.
• In some embodiments the end effector includes jaws. In some embodiments the actuator movement controller includes a ratchet. In some embodiments the state changer includes a movable trigger. In some embodiments with a trigger, the state changer further includes a toggle operatively connected to the trigger so as to be movable with the trigger and to be rotatable with respect to the trigger. In some of the embodiments with a toggle, the toggle is operatively connected to the trigger so as to move with the trigger without rotating with respect to the trigger when the movement controller is enabled. Embodiments of the multi-state ratchet mechanism that controls the end effector and the end effector actuator are disclosed in detail in the U.S. patent application entitled and hereby incorporated “Tool with multi-state ratcheted end effector” by Hinman.
• The embodiments described herein, by way of example, provide an actuator motion controller using a ratchet mechanism that, when engaged, permits the end effector actuator to be moved in one direction (to, e.g., close a pair of jaws) while preventing the end effector actuator to move in the other direction (to, e.g., maintain the jaws in their closed state). InFIG. 3, for example, the ratchet is formed from a rack ofteeth220 extending fromend effector actuator104. Amovable pawl222 is rotatably mounted withinhandle106. A user may change the operation state of the ratchet by operating atrigger224 which connects to pawl222 through atoggle226.
• Returning now to the force limiter,FIGS. 17 and 18 show alternative embodiments of a force limiter according to this invention. Elements common to the embodiment shown inFIGS. 1-20 have been given the same reference numbers. As before,end effector actuator104 and arod actuator502 independently rotate about acommon bushing202. This embodiment replaces the spring of the embodiment shown in correspondingFIGS. 3 and 4 with aspring500 attached torod actuator502.Spring500 engages end effector actuator at anengagement surface504. As in the embodiment shown inFIGS. 1-16,spring500 may be made from a superelastic shape memory material, such as Nitinol, and may be configured by design and/or assembly protocol such that it is pre-loaded to be at or near the plateau in its stress/strain curve. In that way, if a threshold actuation force is met,spring500 deforms to the shape shown, e.g., inFIG. 18 without any additional stress being transmitted through the device's linkage to the end effector.
• FIG. 19 shows yet another alternative embodiment of a force limiter according to the invention in a view that is similar to those ofFIGS. 17 and 18. As before, anend effector actuator104aand a rod actuator602 independently rotate about acommon bushing202. In this embodiment, acoil spring600 comprising a superelastic shape memory material such as Nitinol is pre-loaded and disposed betweenend effector actuator104aand rod actuator602. Pre-loading stress into the spring can place it at or near the plateau in its stress/strain curve, as described above. Consequently, as a threshold actuation force is applied, spring602 deforms it without transmitting any additional stress through the device's linkage to the end effector.
• FIG. 20 shows still another embodiment of a force limiter. In this embodiment, the proximal end of end effector actuation rod125 (optionally formed from Nitinol) is held inrod terminator705. The distal end of aforce limiter700 is also held inrod terminator705, while the proximal end offorce limiter700 is held in aforce limiter housing710.Rod terminator705 fits into a distal opening offorce limiter housing710, but the two parts can be separated, as described below. In this embodiment,force limiter700 is preloaded with a predetermined amount of stress at about or just below the plateau stress of a super elastic material, by, e.g., providing 1.5% strain in the position shown inFIG. 20. The distal portion offorce limiter housing710 is attached to amovable slide member715, which fits in afork720 extending fromend effector actuator704. Whenend effector actuator704 is rotated with a subthreshold force about bushing702,fork720 moves slide715,force limiter housing710,rod terminator705 androd125 proximally to actuate the end effector. If the force applied to endeffector actuator704 exceeds the threshold force (due, e.g., to an object held in end effector jaws),force limiter700 will stretch, separatingforce limiter housing710 fromrod terminator705, so that further movement ofend effector actuator704 will not cause any further movement ofrod125. This feature limits the force delivered by the end effector actuator to the end effector, and consequently the force exerted by the end effector, to the threshold force.
• In yet another embodiment (not shown) similar to that ofFIG. 20, therod125 extends back into the linearly movableforce limiter housing710. By using Nitinol forrod125, or another suitable super elastic material, if the force applied torod125 byend effector actuator704 induces a stress equal to the plateau stress ofrod125, thenrod125 will stretch without increasing the force applied to the end effector.
• While the inventive surgical instruments and devices have been described in some detail by way of illustration, such illustration is for purposes of clarity of understanding only. It will be readily apparent to those of ordinary skill in the art in light of the teachings herein that certain changes and modifications may be made thereto without departing from the spirit and scope of the appended claims. For example, while the force limiter mechanism described herein typically has been in the context of a tool with an articulating mechanism comprising at least two links, the rotation knobs may be used in an instrument comprising only a single link, a multiplicity of links, with any number of cables or cable sets operably connecting the links, or, alternatively, embodiments of the inventive force limiter may be used with surgical instruments that do not articulate at all. Further, while the shaft of depicted instruments including embodiments of the force effector have been depicted as rigid, in some variations it may be desirable to have the handle affixed to a shaft that is flexible. Still further, while the inventive force limiter has been described in the context of a tool comprising a multi-state ratchet mechanism, some embodiments of the force limiter include tools without a ratchet mechanism. Lastly, while the context of the invention is typically understood to be surgical or medical diagnostic procedures, embodiments of the force limiter or tools having such a mechanism may have utility in other, non-medical contexts as well.

Claims (32)

1. A surgical or diagnostic tool comprising:

an end effector at a distal end of the tool;

an end effector actuator at a proximal end of the tool, the end effector actuator being operatively connected to the end effector through a linkage to deliver an actuation force from the end effector actuator to the end effector in response to movement of the end effector actuator; and

a force limiter adapted to establish an upper limit on the actuation force that may be delivered to the end effector by the end effector actuator.

2. The tool ofclaim 1 further comprising a handle supporting the end effector actuator, the end effector actuator being movable with respect to the handle.

3. The tool ofclaim 1 wherein the force limiter comprises a stop element engagable with the end effector actuator to stop its motion.

4. The tool ofclaim 1 wherein the force limiter is adapted to deform in response to actuation force delivered by the end effector actuator.

5. The tool ofclaim 4 wherein the force limiter comprises a spring in the linkage.

6. The tool ofclaim 5 wherein the spring is pre-loaded to a pre-determined stress within the linkage.

7. The tool ofclaim 6 wherein the spring is formed from a superelastic shape memory material treated so as to bend when the upper limit of the actuation force is applied to the end effector by the end effector actuator.

8. The tool ofclaim 7 wherein the superelastic shape memory material has a plateau stress level, the spring being disposed within the linkage so at to be pre-loaded at about the plateau stress level.

9. The tool ofclaim 5 wherein the force limiter further comprises a stop element engagable with the end effector actuator to stop its motion.

10. The tool ofclaim 1 wherein the end effector is operably connected to the end effector actuator at least in part through the force limiter.

11. The tool ofclaim 10 wherein the force limiter is disposed between the end effector actuator and the linkage.

12. The tool ofclaim 10 wherein the end effector actuator is operably connected to the linkage such that movement of the end effector actuator moves the linkage and such that movement of the end effector actuator with respect to the linkage varies when the upper limit of the actuation force is reached.

13. The tool ofclaim 1 where the force limiter comprises a tension bearing member in the linkage, the member comprising a superelastic shape memory material.

14. The tool ofclaim 13 where the tension bearing member is pre-stretched to a pre-determined stress within the linkage.

15. The tool ofclaim 14 where the predetermined stress corresponds to about the upper limit of the actuation force that is to be applied to the end effector by the end effector actuator.

16. The tool ofclaim 1 wherein the end effector comprises a movable force delivery surface.

17. The tool ofclaim 16 wherein the end effector comprises a pair of jaws.

18. The tool ofclaim 1 further comprising:

a shaft disposed between the end effector and the end effector actuator, and

an articulation mechanism for manipulating angular orientation of the end effector with respect to the shaft, the articulation mechanism comprising a proximal link and a distal link spaced apart from the proximal link, such that movement of the proximal link causes corresponding relative movement of the distal link.

19. A method of operating a surgical or diagnostic tool, the tool comprising an end effector in a distal portion and an end effector actuator in a proximal portion, the method comprising:

placing the end effector at a target site;

applying an actuation force to the end effector actuator;

delivering at least some of the actuation force through the end effector to the target site; and

limiting the magnitude of the delivered actuation force to an upper limit.

20. The method ofclaim 19 wherein applying an actuation force comprises moving the end effector actuator.

21. The method ofclaim 20 wherein the tool further comprises a handle supporting the end effector actuator, the step of moving the end effector actuator comprising moving the end effector actuator with respect to the handle.

22. The method ofclaim 20 wherein the tool further comprises a stop element, the moving step comprising engaging the end effector actuator with the stop element.

23. The method ofclaim 19 wherein the tool further comprises a force limiter, the limiting step further comprising deforming the force limiter.

24. The method ofclaim 23 wherein the force limiter comprises a spring, the limiting step comprising deforming the spring.

25. The method ofclaim 24 wherein the deforming step comprises increasing strain of the spring without substantially increasing stress of the spring.

26. The method ofclaim 23 wherein the force limiter comprises a tension bearing member, the limiting step comprising tensioning the member.

27. The method ofclaim 26 wherein the deforming step comprises the tension bearing member stretching in response to tensioning.

28. The method ofclaim 27 wherein the step of limiting the magnitude of the delivered actuation force comprises the stretching of the tension bearing member.

29. The method ofclaim 19 wherein the step of delivering the force comprises moving the end effector, the limiting step comprising ceasing movement of the end effector despite continued movement of the end effector actuator.

30. The method ofclaim 19 wherein the step of delivering the force to the target site comprises moving the end effector.

31. The method ofclaim 30 wherein the end effector comprises jaws, the step of delivering a force to the target site comprising moving the end effector jaws.

32. The method ofclaim 19 wherein the tool further comprises a handle supporting the end effector actuator and a shaft disposed between the handle and the end effector, the method further comprising moving the handle angularly with respect to the shaft to move the end effector angularly with respect to the shaft.

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